Semiaromatic polyamide composite article and processes for its preparation

ABSTRACT

A semiaromatic polyamide composite article comprising a first component comprising a fiber-reinforced material comprising a polyamide composition and reinforcing fibers and having a tensile modulus of at least about 16 GPa as measured by ISO method 527-2:1993 at a rate of 5 mm/min on test specimens having a thickness of 4 mm, a second component comprising a polyamide composition, and an optional tie layer therebetween. The polyamide composition of first component and/or the second component is a semiaromatic polyamide compositions. The second component is prepared by injection molding and/or injection-compression molding the semiaromatic polyamide composition onto the first component.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. National application Ser. No.11/811,043 filed Jun. 8, 2007, which claims the benefit of U.S.Provisional Application No. 60/814,117, filed Jun. 16, 2006.

FIELD OF THE INVENTION

The present invention relates to a semiaromatic polyamide compositearticle comprising a component comprising a fiber-reinforced materialcomprising a polyamide composition, an overmolded component comprising apolyamide composition, and an optional tie layer there between, whereinat least one of the polyamide compositions is a semiaromatic polyamidecomposition.

BACKGROUND OF THE INVENTION

The design flexibility afforded by many thermoplastic compositions andtheir relatively light weights and corrosion resistances make themattractive materials for the replacement of metal components in manyapplications. However, thermoplastic compositions often possess aninsufficient combination of stiffness, strength, toughness and/or otherphysical properties to satisfy the requirements of many of theseapplications. Semiaromatic polyamides, in particular, would be desirablematerials to use in many metal-replacement applications as they canexhibit a roughly constant stiffness over a wide and useful temperaturerange for many applications, including automotive uses. The addition offibrous reinforcing agents to semiaromatic polyamide compositions canproduce materials having good stiffnesses, but this gain is often at theexpense of the toughness of the resulting material. It would thus bedesirable to produce semiaromatic polyamide structures having physicalproperties that rendered them suitable for use as replacements for metalcomponents in various applications.

U.S. Pat. No. 6,644,722 discloses a molded article having a rigidsupport to which is attached a rigid hollow thermoplastic member. U.S.Pat. No. 5,219,642 discloses a structural thermoplastic compositematerial comprising a laminate of a fiber reinforced thermoformablecrystalline polymer composite and an adherent layer of a secondthermoformable polymer. U.S. Re 34,447 discloses crystalline polyamidecompositions and laminates made therefrom. EP 1387760 discloses a methodof production of a fiber-reinforced plastic component.

SUMMARY OF THE INVENTION

There is disclosed and claimed herein a semiaromatic polyamide compositearticle comprising;

-   -   (a) a first component having a surface and comprising a        fiber-reinforced material comprising a polyamide composition and        reinforcing fibers, wherein the first component is not prepared        by injection molding and the fiber-reinforced material has a        tensile modulus of at least about 16 GPa as measured by ISO        method 527-2:1993 at a rate of 5 mm/min on test specimens having        a thickness of 4 mm;    -   (b) an optional tie layer having first and second opposite        surfaces such that when the tie layer is present, the first        surface of the tie layer is in contact with the surface of the        first component; and    -   (c) a second component comprising a polyamide composition,        wherein the polyamide composition of the first component and/or        the polyamide composition of the second component Is a        semiaromatic polyamide composition; and wherein the article is        prepared by a process comprising injection molding and/or        injection-compression molding the composition onto the surface        of the first component when the optional tie layer is not        present and injection molding and/or injection-compression        molding the composition of the second component onto the second        surface of the optional tie layer when the tie layer is present.

DETAILED DESCRIPTION OF THE INVENTION

The articles of the present invention are composite structurescomprising a first component that comprises a fiber reinforced materialcomprising a polyamide composition and reinforcing fibers, and a secondcomponent that comprises a polyamide composition. The structures areformed by injection molding and/or injection-compression molding thepolyamide composition of the second component onto at least one surfaceof the first component. In one embodiment of the invention, the secondcomponent is in direct contact with the surface of the first component.In another embodiment of the invention, a tie layer comprising adifferent material may be present between the second component and allor part of the overmolded surface of the first component. In certainembodiments of the invention, the first component may be encapsulatedwholly or partially by the second component. The polyamide compositionof first component, the second component, or both components is asemiaromatic polyamide composition. The polyamide compositions of thefirst and second components may the same or different. In one embodimentof the invention, the polyamide compositions of the first and secondcomponents are both semiaromatic polyamide compositions. Thesemiaromatic polyamide compositions may be the same or different.

The first component may be formed from the fiber-reinforced material byprocesses such as, but not limited to, one or more of die cutting,stamping, thermoforming, machining, compression molding, and the like.The first component is not prepared by injection molding.

The fiber reinforced material has a tensile modulus of at least about 16GPa, or preferably of at least about 20 GPa, or more preferably of atleast about 30 GPa, as determined by ISO method 527-2:1993 at a rate of5 mm/min on test specimens having a thickness of 4 mm.

The fiber-reinforced material may be formed using any suitable methodknown to those skilled in the art. It may, for example, be in the formof a laminate comprising one or more layers of reinforcing fibers and atleast one polyamide composition where the fiber layers have beenimpregnated by the polymer composition. The laminate may be formed by,for example, laminating polyamide composition sheets and fibers, by, forexample, heat pressing. The fibers may be in any suitable form known tothose skilled in the art, such as woven or nonwoven mats, unidirectionalstrands, and the like and different layers may be formed from differentkinds of fibers and/or any given layer may be formed from two or morekinds of fibers. The fibers may be unidirectional, bi directional, ormultidirectional. Preimpregated unidirectional fibers and fiber bundlesmay be formed into woven or nonwoven mats or other structures suitablefor lamination or other methods of forming the fiber reinforcedmaterial. The fiber-reinforced material may be in the form of aunidirectional preimpregnated material or a multiaxial laminate of apreimpregnated material.

The fibers used in the fiber-reinforced material may be any suitablefiber and may be a mixture of two or more materials. Preferred fibersinclude glass fibers, carbon fibers, and aramid fibers.

In one embodiment of the present application, the composition of thesecond component is injection molded and/or injection-compression moldedonto at least one surface of the first component. The first componentmay be fully or partially encapsulated by the second component. Thefirst component may be inserted into a mold into which the compositionof the second component is injected in molten form. Thus, the secondcomponent is in direct contact with the surface of the first component.

In another embodiment of the present invention, the composition of thesecond component is injection molded and/or injection-compression moldedonto a surface of a tie layer having an opposite surface that is incontact with at least one surface of the first component. In thestructure of the invention, the tie layer is adhered to the first andsecond components. The tie layer may serve to promote adhesion betweenthe first and second components and may comprise one or more polymericcompositions other than the polyamides used in the first and secondcomponents. The tie layer may be in the form of one or more sheetsplaced on the surface of the first component over which the compositionof the second component is injection molded and/or injection-compressionmolded. The tie layer may also be adhered to the surface of the firstcomponent. The tie layer may be added to the surface of the firstcomponent by any method known in the art, such as by laminating one ormore sheets or films comprising the tie layer material to the surface.The tie layer may also be applied to the surface of the first componentby dip coating or spraying.

The second component may also be injection molded and/orinjection-compression molded onto a surface of the first component thatdoes not contain a tie layer and onto a surface of a tie layer having anopposite surface that is in contact with at least one surface of thefirst component.

Examples of materials suitable for use in an optional tie layer includeone or more aliphatic polyamides such as polyamide 6; polyamide 6,6;polyamide 6,10; polyamide 6,12; polyamide 12; polyamide 11; amorphouspolyamides (such as hexamethylene terephthalamide/hexamethyleneisophthalamide copolyamide (6T/6I); and the like. The tie layer maycomprise one or more ionomers. By an ionomer is meant a carboxyl groupcontaining polymer that has been neutralized or partially neutralizedwith bivalent metal cations such as zinc, manganese, magnesium, cadmium,tin(II), cobalt(II), antimony(II), sodium, or lithium and the like.Examples of ionomers are described in U.S. Pat. Nos. 3,264,272 and4,187,358. Examples of suitable carboxyl group containing polymersinclude, but are not limited to, ethylene/acrylic acid copolymers andethylene/methacrylic acid copolymers. The carboxyl group containingpolymers may also be derived from one or more additional monomers, suchas, but not limited to, butyl acrylate. Zinc salts are preferredneutralizing agents. Ionomers are commercially available under theSurlyn® trademark from E.I. du Pont de Nemours and Co., Wilmington, Del.The tie layer may comprise polyurethanes, including thermally activatedpolyurethanes, such as those described in U.S. Pat. No. 5,207,961, whichis hereby incorporated by reference herein.

The polyamide compositions used in the first and second componentscomprise at least one suitable polyamide. Suitable polyamides can becondensation products of dicarboxylic acids or their derivatives anddiamines, and/or aminocarboxylic acids, and/or ring-openingpolymerization products of lactams. Suitable dicarboxylic acids includeadipic acid, azelaic acid, sebacic acid, dodecanedioic acid, isophthalicacid, and terephthalic acid. Suitable diamines includetetramethylenediamine, hexamethylenediamine, octamethylenediamine,nonamethylenediamine, dodecamethylenediamine,2-methylpentamethylenediamine, 2-methyloctamethylenediamine,trimethylhexamethylenediamine, bis(p-aminocyclohexyl)methane,m-xylylenediamine, and p-xylylenediamine. A suitable aminocarboxylicacid is 11-aminododecanoic acid. Suitable lactams include caprolactamand laurolactam.

Suitable polyamides include aliphatic polyamides such as polyamide 6;polyamide 6,6; polyamide 4,6; polyamide 6,9; polyamide 6,10; polyamide6,12; polyamide 10,10; polyamide 11; polyamide 12; and copolymers andmixtures of these polymers.

Examples of suitable aliphatic polyamides include polyamide 6,6/6copolymer; polyamide 6,6/6,8 copolymer; polyamide 6,6/6,10 copolymer;polyamide 6,6/6,12 copolymer; polyamide 6,6/10 copolymer; polyamide6,6/12 copolymer; polyamide 6/6,8 copolymer; polyamide 6/6,10 copolymer;polyamide 6/6,12 copolymer; polyamide 6/10 copolymer; polyamide 6/12copolymer; polyamide 6/6,6/6,10 terpolymer; polyamide 6/6,6/6,9terpolymer; polyamide 6/6,6/11 terpolymer; polyamide 6/6,6/12terpolymer; polyamide 6/6,10/11 terpolymer; polyamide 6/6,10/12terpolymer; and polyamide 6/6,6/PACM (bis-p-[aminocyclohexyl] methane)terpolymer.

Suitable semiaromatic polyamides for use in preparing the compositionsof the second and/or first components may include one or morehomopolymers, copolymers, terpolymers, or higher polymers that arederived from monomers containing aromatic groups. They may also be ablend of one or more homopolymers, copolymers, terpolymers, or higherpolymers that are derived from monomers containing aromatic groups withone or more aliphatic polyamides.

Preferred monomers containing aromatic groups are terephthalic acid andits derivatives, isophthalic acid and its derivatives, andm-xylylenediamine. It is preferred that about 5 to about 75 mole percentof the monomers used to make the aromatic polyamide used in the presentinvention contain aromatic groups, and more preferred that about 10 toabout 55 mole percent of the monomers contain aromatic groups. Thus,preferably, about 5 to about 75 mole percent, or more preferably, 10 toabout 55 mole percent of the repeat units of all polyamides used in thepresent invention contain aromatic groups.

The semiaromatic polyamides may optionally contain repeat units derivedfrom one or more additional aliphatic dicarboxylic acid monomers ortheir derivatives, such as adipic acid, sebacic acid, azelaic acid,dodecanedioic acid, and other aliphatic or alicyclic dicarboxylic acidmonomers having 6 to 20 carbon atoms.

The semiaromatic polyamides may optionally contain repeat units derivedfrom one or more aliphatic or alicyclic diamine monomers having 4 to 20carbon atoms. Preferred aliphatic diamines may be linear or branched andinclude hexamethylenediamine; 2-methyl-1,5-pentanediamine;1,8-diaminooctane; 1,9-diaminononane; methyl-1,8-diaminooctane;1,10-diaminodecane; and 1,12-diaminododecane. Examples of alicyclicdiamines include 1-amino-3-aminomethyl-3,5,5,-trimethylcyclohexane;1,4-bis(aminomethyl)cyclohexane; and bis(p-aminocyclohexyl)methane.

The semiaromatic polyamides may optionally contain repeat units derivedfrom lactams and aminocarboxylic acids (or acid derivatives), such ascaprolactam, 11-aminoundecanoic acid, and laurolactam.

Examples of preferred semiaromatic polyamides include poly(m-xylyleneadipamide) (polyamide MXD,6); hexamethylene adipamide/hexamethyleneterephthalamide copolyamide (polyamide 6,T/6,6); hexamethyleneterephthalamide/2-methylpentamethylene terephthalamide copolyamide(polyamide 6,T/D,T); poly(dodecamethylene terephthalamide) (polyamide12,T); poly(decamethylene terephthalamide) (polyamide 10,T);decamethylene terephthalamide/decamethylene dodecanoamide copolyamide(10,T/10,12); poly(nonamethylene terephthalamide) (polyamide 9,T); thepolyamide of hexamethylene isophthalamide and hexamethylene adipamide(polyamide 6,1/6,6); the polyamide of hexamethylene terephthalamide,hexamethylene isophthalamide, and hexamethylene adipamide (polyamide6,T16,I/6,6); and copolymers and mixtures of these polymers.

The semiaromatic polyamides will preferably have melting points that areat least about 280° C. and is preferably less than about 340° C. Thesemiaromatic polyamide preferably has a glass transition temperature ofat least about 90° C., or more preferably of at least about 110° C., oryet more preferably of at least about 120° C.

The polyamide compositions of the first and second components maycontain additional components such as flame retardants, flame retardantsynergists, impact modifiers, stabilizers (such as oxidation, heat,ultraviolet light, etc. stabilizers), reinforcing agents and fillers(such as glass fibers, glass beads, mineral fibers, mica, talc, and thelike), colorants, plasticizers, thermally conductive additives,electrically conductive additives, lubricants, nucleating agents, andthe like.

The polyamide compositions may be made by melt-blending the componentmaterials using a melt-mixer such as a single or twin-screw extruder,blender, kneader, or Banbury mixer.

The structures of the present invention may be used in a wide variety ofapplications. Examples of automotive applications include seat framecomponents, engine cover brackets, spare tire wells, front-end modules,steering column frames, instrument panels, door systems, body panels(such as horizontal body panels and door panels), engine covers,housings for transmission and power delivery components, oil pans,airbag housing canisters, automotive interior impact structures, enginesupport brackets, cross car beams, bumper beams, pressure vessels suchas refrigerant bottles and fire extinguishers, automotive suspensionwishbone and control arms, suspension stabilizer links, leaf springs,vehicle wheels, recreational vehicle and motorcycle swing arms. Examplesof other applications include appliance (such as washing machine) framesand sports equipment such as inline-skate components, baseball bats,hockey sticks, ski and snowboard bindings, and bicycle frames

EXAMPLES

“PPA” refers to a hexamethylene terephthalamide/2-methylpentamethyleneterephthalamide semiaromatic polyamide.

“PA 6,6” refers to polyamide 6,6 and “PA 6” refers to polyamide 6.

Tensile properties were measured according to ISO 527 using a strainrate of 5 mm/min. Unnotched Charpy impact strengths were measuredaccording to ISO 179. The faces of the bars were impacted.

Storage modulus was measured at 25° C. and 125° C. using a dynamicmechanical analyzer (TA Instruments Q800 DMA) under a three point flexconstant load geometry. The temperature was increased at 2° C./min,frequency 1 Hz and amplitude of 10 micrometers. The percentage retentionof storage modulus at 125° C. relative to that at 25° C. is reported inTable 2.

Examples 1 and 2 and Comparative Example 1

Laminates were prepared by compression molding a stack of nine layers ofpolymeric film alternating with nine layers of woven continuous glassfiber sheets into a 2 mm thick sheet. In the case of Example 1, thepolymeric film was semiaromatic polyamide, and in the case of Example 2,it was polyamide 6,6.

The laminates were cut into 1.5 in×6 in rectangular bars and placed inthe cavity of an injection molding machine. In each case, after it waspreheated to 150° C., the laminate was overmolded with semiaromaticpolyamide such that the resulting part had a thickness of about 0.125in. In the case of Comparative Example 1, no laminate was used andsemiaromatic polyamide was injection molded into parts having the samethickness as those prepared from the laminates.

The resulting molded parts were cut with a water jet into the requiredgeometry for the determination of tensile properties and unnotchedCharpy impact strengths and the corresponding test results are shown inTable 1. Impact testing was done wherein parts from Examples 1 and 2were impacted on the laminate face or the overmolded face. The resultsfrom each are reported in Table 1. In the case of Comparative Example 1there was no laminate face, so a single impact strength is reportedunder the heading of “overmolded face”.

TABLE 1 Example 1 Example 2 Comp. Ex. 1 Laminate PPA PA 6,6 — Overmoldedpolymer PPA PPA PPA Tensile strength 156 160 112 (MPa) Elongation atbreak 2 1.2 1 (%) Tensile modulus 16 15.2 11.5 (GPa) Unnotched Charpyimpact strength (kJ/m²) Laminate face 92 172 — Overmolded face 123 12960

Examples 3-6 and Comparative Examples 2-6

Laminates were prepared from polymer films and woven continuous glassfiber sheets in a manner similar to that described above for use inExamples 3-6 and Comparative Examples 2 and 4. The polymeric films usedare those indicated in Table 2 under the heading of “Laminate”. Thelaminates were overmolded with the polymer indicated in Table 2 asdescribed above, except that the inserted laminates were heated to 200°C. before overmolding. The thickness of the overmolded part is given inTable 2. The overmolded specimens were cut using a water jet into 13×60mm bars that were used for storage modulus testing.

TABLE 2 Comp. Comp. Comp. Comp. Comp. Ex. 3 Ex. 2 Ex. 3 Ex. 4 Ex. 4 Ex.5 Ex. 5 Ex. 6 Ex. 6 Laminate PA 6, 6 PA 6, 6 — PPA PA 6 — PPA PA 6, 6 —Overmolded polymer PPA PA 6, 6 PA 6, 6 PA 6, 6 PA 6, 6 PA 6, 6 PPA PPAPA 6, 6 Part thickness (in.) 0.1875 0.1875 0.1875 0.125 0.125 0.1250.125 0.125 0.125 Storage modulus at 25° C. 12 11.4 10.3 9.7 9.6 9.5 9.39.3 9.5 (GPa) Storage modulus at 125° C. 8.4 5.4 4.6 5.6 4.3 4.3 8.6 7.14.3 (GPa) Retention of modulus (%) 70 47 45 58 45 45 93 77 45

Examples 7 and 8

10 mil films of PPA and an ionomer (Surlyn® 9320, supplied by E.I. duPont de Nemours Inc., Wilmington, Del.) were prepared by melting solidpolymer in a 28 mm twin screw and extruding it through a film die onto acasting drum. 10 mil laminates were prepared by compression moldingalternating sheets of PPA film and sheets of woven continuous carbonfibers for 8 minutes under 8 Kpsi of pressure in a press in which thetop and bottom plattens had been heated to 180° C. In the case ofExample 8, ionomer film was laminated to one surface of the PPA/carbonfiber sheet laminate. The laminates of Example 7 (which had no ionomertie layer) and Example 8 were placed in the mold cavity of an injectionmolding machine and overmolded with PPA. In the case of Example 8, thesample was positioned such that the surface comprising the ionomer filmwas overmolded. The mold cavity temperature was set at 100° C.; thebarrel temperatures were set to 310° C.; and the melt temperature of thePPA was about 320-330° C. The laminates were not preheated.

In the case of Example 7, there was no adhesion between the laminate andthe overmolding; they came apart to the touch. The adhesion between thelaminate and the overmolded PPA resin was in the case of Example 8 wasstudied by peel testing in an Instron. The specimens exhibited a peakload of 15.6 lbf; a peak stress of 10.4 lbf/in; and a peel strength of4.9 lbf/in.

1. A process for the preparation of a semiaromatic polyamide compositearticle, comprising the steps of: (a) preparing by a non-injectionmolding process a first component having a surface and comprising afiber-reinforced material comprising a polyamide composition andreinforcing fibers, wherein the fiber-reinforced material has a tensilemodulus of at least about 16 GPa as measured by ISO method 527-2:1993 ata rate of 5 mm/min on test specimens having a thickness of 4 mm; (b)injection molding and/or injection-compression molding a polyamidecomposition onto the surface of the first component to form a secondcomponent; wherein the polyamide composition of the first componentand/or the polyamide composition of the second component Is asemiaromatic polyamide composition, said method further comprisingcomprising injection molding and/or injection-compression molding thecomposition of the second component onto the surface of the firstcomponent when the optional tie layer is not present and injectionmolding and/or injection-compression molding the composition of thesecond component onto the second surface of the optional tie layer whenthe tie layer is present, and wherein the semiaromatic polyamidecomposite article has at least a 58% retention of storage modulus at125° C. relative to the storage modulus at 25° C.
 2. The process ofclaim 1, wherein the fiber-reinforced material is a laminate.
 3. Theprocess of claim 1, wherein the first component is prepared from thefiber-reinforced material by one or more of die cutting, stamping,thermoforming, machining, and/or compression molding.
 4. The process ofclaim 1, wherein the reinforcing fibers are selected from one or more ofglass fibers, carbon fibers, and aramid fibers.
 5. The process of claim1, wherein the polyamide composition of the second component is asemiaromatic polyamide composition comprising one or more ofpoly(m-xylylene adipamide) (polyamide MXD,6); hexamethyleneadipamide/hexamethylene terephthalamide copolyamide (polyamide 6,T/6,6);hexamethylene terephthalamide/2-methylpentamethylene terephthalamidecopolyamide (polyamide 6,T/D,T); poly(dodecamethylene terephthalamide)(polyamide 12,T); poly(decamethylene terephthalamide) (polyamide 10,T);decamethylene terephthalamide/decamethylene dodecanoamide copolyamide(10,T/10,12); poly(nonamethylene terephthalamide) (polyamide 9,T); thepolyamide of hexamethylene isophthalamide and hexamethylene adipamide(polyamide 6,I/6,6); and/or the polyamide of hexamethyleneterephthalamide, hexamethylene isophthalamide, and hexamethyleneadipamide (polyamide 6,T/6,I/6,6).
 6. The process of claim 1, saidmethod the steps of adhering to or positioning in contact with thesurface of the first component a first surface of a tie layer beforeperforming step (b).
 7. The process of claim 1, the composition of saidtie layer is an semiaromatic polyamide composition comprising one ormore of poly(m-xylylene adipamide) (polyamide MXD,6); hexamethyleneadipamide/hexamethylene terephthalamide copolyamide (polyamide 6,T/6,6);hexamethylene terephthalamide/2-methylpentamethylene terephthalamidecopolyamide (polyamide 6,T/D,T); poly(dodecamethylene terephthalamide)(polyamide 12,T); poly(decamethylene terephthalamide) (polyamide 10,T);decamethylene terephthalamide/decamethylene dodecanoamide copolyamide(10,T/10,12); poly(nonamethylene terephthalamide) (polyamide 9,T); thepolyamide of hexamethylene isophthalamide and hexamethylene adipamide(polyamide 6,I/6,6); and/or the polyamide of hexamethyleneterephthalamide, hexamethylene isophthalamide, and hexamethyleneadipamide (polyamide 6,T/6,I/6,6)
 8. The process of claim 7, wherein thetie layer comprises one or more polyamides, ionomers, and/orpolyurethanes.
 9. The process of claim 7, wherein the tie layercomprises one or more of polyamide 6; polyamide 6,6; polyamide 6,10;polyamide 6,12; polyamide 12; polyamide 11; and amorphous polyamides.10. The process of claim 1 or 7, wherein the polyamide composition ofstep (a) comprises at least one semiaromatic polyamide.